My experience is slightly different. Though not with Zarina (a Character Disney just forgot and has never been represented in the parks at all).
But I find the characters are very well versed in all the movies their character was in.
For instance,
Ariel will be fully aware she has a daughter named Melody.
Step Sisters will be fully aware of their activities in the Cinderella sequels. Anastasia is aware she fell in love with a Baker, for instance.
Now, they won't bring them up unless you do but they won't be totally unaware of them either. And of course, some are more diligent about remembering their characters activities than others. But the good thing is they are all great at improv so they can fake it
The problem with Zarina is she was just forgotten by Disney so few even know about the character at all. They really should train Tink, Hook and Pan about her.